The joints in our body are also referred to as “articulations”, as they consist of multiple bones interacting, or “articulating” with one another. In order for our body to execute the big motions we need for function, such as lifting our arm above our head, the bones articulating in our joints undergo subtle types of movement, termed: “arthrokinematics”. In this post I’ll break down the influence of arthrokinematics, how injuries can affect their movement patterns, and some specifics on how it’s affected my shoulder rehab.
OSTEOKINEMATICS vs ARTHROKINEMATICS
These $10 words both contain the root “kinematics”, meaning motion. They differ in that “osteo-“ kinematics refers to the motion observed by the whole bone; whereas “arthro-“ kinematics details the actual movement of the joint surfaces. Osteokinematics are the large motions of our bones we can sense, feel, and observe, while arthrokinematics are the relative, subtle motions of the bones articulating together in a joint. In order to have full osteokinematic motion (i.e. full range of motion), it is crucial to have full arthrokinematic motion. Thus, if you lack a particular arthrokinematic motion in a joint, you will not have full range of motion in that joint.
For example, shoulder flexion is the movement of raising your arm above your head in front of you (think reaching to grab something over your head on a kitchen shelf). The movement of shoulder flexion, is the osteokinematic motion, whereas the subtle roll and slide that occurs between the humerus and scapula are arthrokinematic motions. Though we can’t feel arthrokinematic motion when it occurs, if it didn’t we’d experience a sharp, pinching pain somewhere around the midpoint of that reaching motion. From an arthrokinematic standpoint, our ability to have full shoulder flexion range of motion, is dependent on having full arthrokinematic motion.
TRAUMATIC INJURY & ARTHROKINEMATICS
The arthrokinematic pattern at each joint is dictated by the shape and condition of each bone’s articulating joint surfaces. Most healthy joint surfaces are slightly round (either concave or convex), and are lined with articular cartilage to promote smooth, frictionless motion between the bones. The glenohumeral (shoulder) joint, is composed of a convex humeral head articulating with a concave glenoid fossa.
If your body experiences a traumatic injury, such as a shoulder dislocation, it can significantly impact the quality and relationship of the articulating surfaces in that joint. As joint surfaces are now altered, this influences its arthrokinematic pattern and greatly decreases its longevity. As the joint surfaces no longer move as efficiently as they did pre-injury, it accelerates the “wearing out” of a joint and can lead to an earlier onset of osteoarthritis. This can apply to any joint in the body, with the current discussion around LA Rams running back Todd Gurley’s knee serving as a relevant example.
With regards to shoulder anatomy , I detailed the golf ball and tee analogy in my last post (link here). With an arthrokinematic discussion, it may be easier to picture by thinking of a cue ball and a pool table. A healthy shoulder resembles that of a new cue ball on fresh felt, rolling smooth and true. In an arthritic shoulder, that cue ball may have a few chips in it while the table felt may have some rips and dents.
CURRENT IMPLICATIONS
Prior to my surgery, the severity and extent of osteoarthritis caused a significant loss of both quantity and quality of arthrokinematic motion between my humeral head and glenoid. As I detailed in that last post, the condition of my shoulder after surgery resembled that of a new golf ball on a broken down, but remodeled golf tee. Translated to the pool analogy, I’ve got a fresh cue ball but the table felt is pretty worn down.
Fortunately, with this new cue ball comes a new opportunity to regain a more efficient arthrokinematic pattern. Moving forward I’ll detail some of the specific joint mobilization work I’ve implemented along the way and how that’s translated for me functionally.
Thanks for the read y’all! As always, feel free to reach out with any questions and please share if you know anyone this might resonate with.
Much love y’all,
Nate